The fact is currently known that the comfort of a shoe is linked not only to correct anatomically fitting properties but also to correct outward permeation of the water vapor formed inside the shoe due to perspiration.
Traditionally, vapor-permeable shoes are those which use natural materials such as leather or equivalent products, which however, in the presence of rain or bad weather, because of their vapor-permeable properties, do not ensure good waterproofness and indeed absorb water rather easily.
For this reason, shoes with an upper made of leather (or the like) associated to a lining with a vapor-permeable and waterproof membrane (made for example of a material such as expanded polytetrafluoroethylene, e-PTFE, polyurethane, PU, or the like), sewn or glued to an insole, have now been in use for several years.
Moreover, as is known, however, most of the perspiration of the foot is generated at the interface between the sole of the foot and the sole of the shoe, which is typically made of polymeric material.
It is evident that the perspiration that has formed on such interface is unable to evaporate, accordingly condensing on the footbed on which the foot rests; only a minor percentage of the perspiration evaporates through the upper.
Accordingly, shoes have now been devised for years which have vapor-permeable and waterproof soles (such as for example the one disclosed in Italian patent no. 1,282,196), which are associated with waterproof and vapor-permeable uppers such as the ones described above, in order to provide shoes that are completely waterproof and vapor-permeable.
A shoe of this type is disclosed for example in WO097/14326.
The shoe disclosed in WO097/14326 in practice has a sole provided with a tread with holes and a membrane which is waterproof and vapor-permeable, covers the holes and is joined perimetrically and hermetically to the tread, so as to not allow infiltrations of water.
This sole ensures correct vapor permeation in addition to an effective exchange of heat and water vapor between the environment inside the shoe and the outside environment, at the same time ensuring the necessary tightness with respect to external moisture and water, in a manner similar to what is performed by the upper with which the membrane is associated.
In this shoe configuration, the sole and the upper are two distinct parts, both of which are vapor-permeable and waterproof, which are associated and sealed one another so as to avoid the rise of water in the connecting points.
The soles used in these shoes are therefore structured so as to allow vapor permeation but not the passage of water from outside inwardly; the structure of the sole is therefore more complicated than a traditional sole, and this complexity arises from the accommodation of the membrane and from the correct perimetric sealing of the latter with respect to the sole.
Usually, the structure of the upper of shoes of the described type is very complicated with respect to a traditional upper and this complexity arises from the need to fold the lining with the membrane onto itself so as to allow its sealing with an additional membrane arranged below the insole or from the need to have a lining with a membrane that is larger than the upper, so as to provide a perimetric seal of the latter with the sole.
Resorting to these solutions leads to some drawbacks that the shoe thus provided has: creases in fact form easily in the lining with membrane, whether folded or not, at the toe and at the heel, to the full detriment of an easy sealing of the membranes of the upper and of the one arranged at the insole.
In general, regardless of whether the sole is vapor-permeable or not, in the manufacture of these shoes it is important to pay attention to the sealing of the connecting regions between the insole, the lining with membrane and the sole, in order to avoid even the slightest seepage of water from outside.